I live in the land of late freezes. We live at 3,600′ at the base of the Cascade mountains in what is basically the desert. Once it clears off at night, it’s normal for temperatures to drop into the high 20’s. We’ll normally get some level of frost for many nights before bloom time. It’s been my experience that buds remain more resistant to damage if it gets cold every night. In contrast, if we have a few warm nights, then we are headed for trouble. We’ve gotten temperatures in the teens before, and still not lost flowers. But again, our flowers are “conditioned” it seems, by constant exposure to low temperatures in the evenings. One other result is that our plants are much shorter than the same varieties grown elsewhere.
The main damage I worry about as a hybridizer is carpal damage. In my experience, carpals are much more susceptible to damage than the flowers themselves. Flowers will bloom, by outward appearances the carpals will look good, only to shrivel up into nothing a week or so after the flowers have bloomed. Or the carpals will stay good, but have no seeds in them.
Of the tetraploids I have here, Salmon Dream seems to be the most resistant to frost damage. Lemon Chiffon is somewhat more susceptible, but often it’s sidebuds will be undamaged. Blushing Princess is much more susceptible to frost damage, while Vanilla Schnaps is pretty much useless. The same can be said for Mackinac Grand : it’s probably the most susceptible to carpal damage of any peony I grow. All of these will make generally make flowers, but seed production is always questionable. I have a few that I cover now, with sheets and big jugs of hot water in the evenings, and as a result, I’m able to get some seeds on Sugar n’ Spice, as well as Laddie. But covering things, and filling water jugs gets tiresome after a while. The folks at the nursery where my seedlings are grown on are getting tired of seeing so many Salmon Dream hybrids, but the reason is because SD is so frost resistant.
I’m bringing home some of my own hybrids too now, and it’s hard to say what their frost resistance is like. Once Blushing Princess is crossed with some other things, it’s seedlings may be more frost tolerant. I’m hoping that will be the case, as it’s a producer of particularly vigorous seedlings, and seedlings that are often quite upright as well.
Don mentioned seedlings which emerge with their buds quite developed, and I can agree that this may be an early seed maturing strategy, but once such species get crossed, they may bring this emergence habit with them, but leave the frost resistance behind.
Vanilla Schnaps, I’m talking about you !